Cryogenic refrigerator

ABSTRACT

In a cryogenic refrigerator using a Gifford MacMahon (GM) cycle, a rotary valve device (RV) for controlling the supply and discharge of refrigerant gas with respect to the refrigerator (2) is adapted by a reversible motor (15) to be rotated in normal and reverse directions, and during the rotation in the normal direction, a cooling mode operation for producing cold by an adiabatic expansion is effected, and during the rotation in the reverse direction, a temperature-raising mode operation for producing heat by an adiabatic compression is effected. In order that the optimum efficiency can be obtained in each of the cooling mode operation and the temperature-raising mode operation, the timing of opening and closing of the rotary valve device (RV) with respect to the reciprocal movement of displacers (3a, 3b) during the rotation in the normal direction is made different from said timing during the rotation in the reverse direction. As a result, the time required for raising the temperature of a cooling portion in a cryogenic condition to the normal temperature can be shortened without the need for any special equipment.

TECHNICAL FIELD

This invention relates to a cryogenic refrigerator using a Gifford MacMahon (GM) cycle or the like, and more particularly to a cryogenic refrigerator having the function of raising the temperature of a cooling portion in a cryogenic condition to the normal temperature.

For example, in a cryopump using a cryogenic refrigerator utilizing a Gifford MacMahon cycle, for raising the temperature of a cooling portion to the normal temperature, there have heretofore been used a method of introducing dry nitrogen gas into a vacuum vessel and a method of flowing electric current through a heater, provided at the cooling portion, to produce Joule heat by which the temperature is raised; however, either of these methods requires some special equipment, and besides has a problem that a panel temperature does not rise quickly.

Therefore, there has been proposed in U.S. Pat. No. 4,520,630, a method in which a drive motor for a refrigerator is reversely rotated to operate a refrigeration cycle reversely, thereby raising the temperature. This method has a problem that during a temperature-raising mode operation, the phase of a displacer becomes inconsistent with a valve opening-closing timing, so that a sufficient temperature-raising effect can not be obtained.

DISCLOSURE OF THE INVENTION

It is an object of this invention to provide a cryogenic refrigerator using a Gifford MacMahon (GM) cycle, in which the time required for raising the temperature of a cooling portion to the normal temperature can be shortened using a method of reversely operating a refrigeration cycle, without the use of any special equipment for raising the temperature of the cooling portion.

In order to achieve the above object, according to the present invention, there is provided a cryogenic refrigerator of the Gifford MacMahon cycle-type comprising at least one cylinder; at least one displacer which has a regenerator therein and is reciprocally movable within the cylinder; upper and lower empty chambers provided within the cylinder and disposed exteriorly of opposite ends of the displacer, the both empty chambers being communicated with each other via the regenerator within the displacer; a rotary valve device for controlling the flow of refrigerant gas under high pressure into the empty chambers and for controlling the flow of the refrigerant gas under low pressure from the empty chambers; and a reversible motor for rotating the rotary valve device in normal and reverse directions and for controlling the reciprocal movement of the displacer, wherein when the rotary valve device is rotated in the normal direction, the refrigerant gas in the lower empty chamber is subjected to an adiabatic expansion to produce cold, and when the rotary valve device is rotated in the reverse direction, the refrigerant gas in the lower empty chamber is subjected to an adiabatic compression to produce heat; the cryogenic refrigerator being characterized by the provision of means by which the timing of opening and closing of the rotary valve device with respect to the reciprocal movement of the displacer during the rotation in the normal direction is made different from the timing during the rotation in the reverse direction.

In a preferred embodiment of the present invention, the rotary valve device comprises a fixed valve body, and a valve plate rotatably supported in face-to-face contact with the valve body, and the means by which the timing of opening and closing of the rotary valve device with respect to the reciprocal movement of the displacer during the rotation in the normal direction is made different from the timing during the rotation in the reverse direction comprises an engagement groove formed in a rear surface of the valve plate and extending circumferentially over a predetermined angle, and a pin portion provided on a crank driven by the reversible motor and engaged in the engagement groove in the valve plate. Therefore, there is provided a feature that during the rotation of the crank in a normal or a reverse direction, the valve plate does not rotate but idles until the pin portion is brought into engagement with one or the other end of the engagement groove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a refrigerator of the Gifford MacMahon cycle-type according to the present invention;

FIG. 2 is an end view of a valve plate of a rotary valve device used in the above refrigerator, taken along the line II--II of FIG. 1;

FIG. 3 is an exploded, perspective view showing a drive mechanism for the valve plate and a Scotch yoke;

FIG. 4 is an exploded, perspective view showing the valve plate and a valve body constituting the rotary valve device;

FIG. 5 is a diagram of a motor connection wiring of a conventional refrigerator of a Gifford MacMahon cycle-type; and

FIG. 6 is a diagram of a motor connection wiring of the refrigerator of a Gifford MacMahon cycle-type according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIG. 1, a compressor 1 draws refrigerant gas from a low-pressure side 1a, increases a pressure thereof, cools it, and then discharges it to a high-pressure side 1b.

A refrigerator 2 is divided into a housing portion 23 and a cylinder portion 10. Displacers 3a, 3b, which are integral with each other and contain regenerators 4, 5, respectively, are slidably received respectively in upper and lower cylinders 10a, 10b arranged in a two-stage manner. Empty chambers 11 (first-stage lower empty chamber), 12 (second-stage lower empty chamber) and 13 (upper empty chamber) are formed between the displacers 3a, 3b and the cylinders 10a, 10b. The empty chambers 11, 12, 13 are communicated with one another through the displacers 3a, 3b, containing the respective regenerators 4, 5, and refrigerant gas passages L1˜L4. Flanges 6, 7 are held in intimate contact respectively with the outer peripheries of the lower portions of the cylinders 10a, 10b in heat-transferring relation thereto.

The displacers 3a, 3b are connected to a Scotch yoke 22 supported by sliding bearings 17a, 17b, and are driven through a reversible motor 15, a crank 14 and the Scotch yoke 22 to reciprocally move within the cylinders 10a, 10b, respectively. When the volumes of the empty chambers 11, 12 within the cylinders 10a, 10b increase in accordance with the reciprocal movement of the displacers 3a, 3b, the volume of the empty chamber 13 decreases, and when the volumes of the empty chambers 11, 12 decrease, the volume of the empty chamber 13 is so changed as to increase, and refrigerant gas moves between the empty chambers 11, 12, 13 through the refrigerant gas passages L1˜L4.

A rotary valve device RV for controlling the flow of the refrigerant gas is provided between the compressor 1 and the cylinders 10a, 10b, and is so constructed as to guide the refrigerant gas, fed from the high-pressure side 1b of the compressor 1, into the cylinders 10a, 10b, and also to guide the refrigerant gas, fed from the cylinders 10a, 10b, to the low-pressure side 1a of the compressor 1.

The rotary valve device RV comprises a valve body 8, and a valve plate 9, and the valve body 8 is fixedly mounted within the housing by a fixing pin 19. As shown in FIGS. 2 and 3, the valve plate 9 has an engagement groove 16 which is formed in a circumferential direction (in the embodiment, the angle in the circumferential direction is 280°) and is engaged with a pin portion 14a of the crank 14 which drives the Scotch yoke 22. When the pin portion 14a is engaged with an end 16a or an end 16b of the engagement groove 16 upon rotation of the crank 14 in its normal or its reverse direction, the motion of the crank 14, that is, the rotation of a reversible motor shaft 15a, is transmitted to the valve plate 9 to rotate the valve plate 9. The engagement groove 16 in the circumferential direction and the pin portion 14a connect the valve plate 9 and the reversible motor shaft 15a together in such a manner that idling occurs between the normal rotation and the reverse rotation through an angle of 280° in this embodiment.

A refrigerant gas intake hole 8b is formed through the central portion of the valve body 8, and is connected to the high-pressure side 1b of the compressor 1. As shown in FIG. 4, an arcuate groove 8c is formed in an end face 8a facing the valve plate, and is disposed in concentric relation to the intake hole 8b. There is formed a communication hole 8d which is open at one end thereof to the groove 8c and is extended through the body 8 to be communicated at the other end thereof with a discharge port 8e open to the side surface of this body. The discharge port 8e is open to the empty chamber 13 via a passage 20. A groove 9d is formed in an end face 9a of the valve plate 9 facing the valve body, and extends radially from its center. An arcuate hole 9c is formed through the valve plate 9 to extend from the end face 9a to the opposite end face 9b, and is disposed on the same circumference as that of the arcuate groove 8c in the valve body 8. An intake valve is constituted by the intake hole 8b, the groove 9d, the arcuate groove 8c and the communication hole 8d, and an exhaust valve is constituted by the communication hole 8d, the arcuate groove 8c and the arcuate hole 9c.

A wiring of connection of the above reversible motor, as well as the direction of rotation thereof, is shown in FIG. 5. Namely, in a conventional refrigerator, the motor shaft 15a is caused by a switch Sa to rotate only in a normal direction. On the other hand, by the provision of a changeover switch Sb, the direction of rotation of the motor shaft 15a in the present invention can be switched between a CW contact (rotation in a normal direction) in a cooling mode and a CCW contact (rotation in a reverse direction) in a temperature-raising mode.

The operation in the cooling mode is effected by the rotation of the reversible motor 15 in the normal direction. At this time, the pin portion 14a of the crank 14 is engaged with one end 16a of the engagement groove 16 in the valve plate 9 to rotate the valve plate 9 in the normal direction.

Before the displacers 3a, 3b reach a bottom dead center LP (in the embodiment, when they reach a position an angle of 20° before the bottom dead center), the exhaust valve is closed, and also a passage is formed between the communication hole 8d, the arcuate groove 8c and the groove 9d (the intake valve is opened), and the refrigerant gas under a high pressure begins to fill in the empty chamber 13 via the passage 20 in the housing. Namely, the intake valve is already in an open condition before the displacers 3a, 3b reach the bottom dead center. The displacers 3a, 3b pass past the bottom dead center, and begin to move upward, and the refrigerant gas passes downward through the regenerators 4, 5 to fill in the empty chambers 11, 12.

Before the displacers 3a, 3b reach a top dead center UP (in the embodiment, when they reach a position an angle of 65° before the top dead center), the intake valve is closed. Before the displacers 3a, 3b reach the top dead center (in the embodiment, when they reach a position an angle of 45° before the top dead center), a passage is formed between the communication hole 8d, the arcuate groove 8c and the arcuate hole 9c (the exhaust valve is opened). The refrigerant gas under high pressure undergoes an adiabatic expansion to produce cold to cool the flanges 6, 7, and moves upward while cooling the regenerators 4, 5, and begins to be returned to the low-pressure side 1a of the compressor 1.

Before the displacers 3a, 3b reach the bottom dead center LP (in the embodiment, when they reach a position an angle of 20° before the bottom dead center), the exhaust valve is closed, and the intake valve is opened, thus finishing one cycle.

The operation in a temperature-raising mode is effected by the rotation of the reversible motor 15 in the reverse direction. In contrast with the cooling mode operation, the pin portion 14a of the crank 14 is engaged with the other end 16b of the engagement groove 16 in the valve plate 9 to rotate the valve plate 9 in the reverse direction.

When the displacers 3a, 3b reach a position before the top dead center UP (that is, a position 35° before the top dead center in the embodiment), the exhaust valve is closed, and further when they reach a position before the top dead center (that is, a position 15° before the top dead center in the embodiment), a passage is formed between the communication hole 8d, the arcuate groove 8c and the groove 9d (the intake valve is opened), and the refrigerant gas under high pressure pass through the regenerators 4, 5 via the passage 20 in the housing to fill in the empty chambers 11, 12, and the temperature of the flanges 6, 7 in a low-temperature condition is raised by a compression heat (adiabatic compression work at the time of filling of the gas) produced at this time.

Before the displacers 3a, 3b reach the bottom dead center (in the embodiment, when they reach a position an angle of 60° before the bottom dead center), the intake valve is closed, and at the same time a passage is formed between the communication hole 8d, the arcuate groove 8c and the arcuate hole 9c (the exhaust valve is opened), and the refrigerant gas in the empty chamber 13 undergoes an adiabatic expansion to produce cold. The refrigerant gas under low pressure which has decreased in temperature is discharged directly into the housing 23 and is returned to the low-temperature side 1a of the compressor 1a, without effecting a heat exchange with the regenerators 4, 5.

When the displacers 3 reach a position before the top dead center (that is, a position 35° before the top dead center in the embodiment), the exhaust valve is closed, thus finishing one cycle.

CAPABILITY OF EXPLOITATION IN INDUSTRY

In a conventional method in which at the time of regenerating a cryopump, the operation of a refrigerator is stopped, and then heat is supplied by heated gas, a heater or the like to a surface of a cryo-panel from the exterior, the temperature of a regenerator within a displacer can not be raised easily, and therefore much time is required for raising the panel temperature. In the present invention, however, the refrigerant gas is subjected to an adiabatic compression within the cylinder of the refrigerator to produce heat, and therefore the temperature of the regenerators in the displacers is first raised, and besides in the temperature-raising mode operation, the opening and closing of the intake valve and the exhaust valve of the refrigerator are automatically adjusted to an optimum timing for effecting the temperature-raising operation, and therefore the time required for raising the temperature of the cryo-panel can be greatly reduced. 

We claim:
 1. A cryogenic refrigerator of the Gifford MacMahon cycle-type comprising at least one cylinder; at least one displacer which has a regenerator therein, and is reciprocally movable within said cylinder; empty chambers provided within said cylinder, and disposed exteriorly of opposite ends of said displacer, said empty chambers being communicated with each other via said regenerator within said displacer; a rotary valve device for controlling the flow of refrigerant gas under high pressure into said empty chambers and for controlling the flow of refrigerant gas under low pressure from said empty chambers, said rotary valve device including a fixed valve body and a valve plate rotatably supported in face-to-face contact with said valve body; and a reversible motor for rotating said rotary valve device in normal and reverse directions and for controlling the reciprocal movement of said displacer, said reversible motor driving a crank, wherein when said rotary valve device is rotated in the normal direction, the refrigerant has in the lower empty chamber is subjected to an adiabatic expansion to produce cold, and when the rotary valve device is rotated in the reverse direction, the refrigerant gas in the lower empty chamber is subjected to an adiabatic compression to produce heat; and means by which the timing of opening and closing of said rotary valve device with respect to the reciprocal movement of said displacer during rotation in the normal direction is made different from said timing during rotation in the reverse direction, said means comprising an engagement groove formed in a rear surface of said valve plate and extending circumferentially over a predetermined angle, and a pin portion provided on said crank driven by said reversible motor and engaged in said engagement groove in said valve plate, whereby during rotation of said crank in a normal or reverse direction, said valve plate does not rotate but idles until said pin portion is brought into engagement with one or the other end of said engagement groove.
 2. A cryogenic refrigerator according to claim 1, in which said engagement groove is formed in such a manner that said idling is effected through about 280°. 